You can use the imagepatternedline() function with extra features instead of imagedashedline() to give a visible dashedlines and other any kind of patterned lines on your images. The routine also manages the thickness of the line. Have fun!

<?php
// imagepatternedline() function
// Routine was developed to draw any kind of straight line with thickness. Routine uses imageline() function to draw line.
// Parameters are (similar to imageline() function):
// $image: (resource) imagefile
// $xstart, $ystart: (int) x,y coordinates for first point
// $xend, $yend: (int) x,y coordinates for last point
// $color: (int) color identifier that created with imagecolorallocate()
// extra parameters:
// $thickness: (int) thickness of line in pixel
// $pattern: (string) pattern of line, which repeats continuously while line is being drawed.
// If there is '1' in the pattern that means the actual dot of line is visible,
// '0' means dot is not visible (space between two line elements).
// All characters regard for one pixel. Default: 1 dot wide dashed line with 4-4 dots and spaces.
// Examples for pattern:
// "1" or "" continuous line
// "10" close dotline
// "10000" dotline
// "111111110000001100000011111111" dotline for design drawing
// "111111111100000011000000110000001111111111" double dotline
// some examples for using imagepatternedline():
// imagepatternedline($image,300,300,442,442,$color,200,""); // a square with 200 length of edge and rotated 45 degrees
// imagepatternedline($image,100,200,289,200,$color,100,
// "11001100000011001111000011001111110000001100001100"
// ."00001111001100111100000011000000110000110011001100"
// ."11000011111100111111000011001111001111000011110000"
// ."1111001111110011000011000000001100110011"); // barcode